Method and apparatus for exhaust aftertreatment in a spark-ignition direct-injection internal combustion engine

ABSTRACT

The disclosure sets forth a spark-ignition, direct-fuel injection internal combustion engine selectively operative at an air/fuel ratio lean of stoichiometry and fluidly connected to an exhaust aftertreatment system. The exhaust aftertreatment system consists essentially of an electro-thermal heating element adjoining a converter element. A control system comprising a control module is signally connected to a sensing device and adapted to monitor a temperature of the converter element and operatively connected to the engine and operative to connect the electro-thermal heating element to an electric power source.

TECHNICAL FIELD

This disclosure is related to exhaust aftertreatment systems for spark-ignition direct-injection internal combustion engines.

BACKGROUND

Known aftertreatment systems for spark-ignition internal combustion engines that operate lean of stoichiometry include one or more three-way catalytic converters mounted in close proximity to the engine and a NOx adsorber converter, also referred to as a lean NOx trap (hereafter ‘LNT device’) mounted in an underfloor location. Known three-way catalytic converters function to reduce engine-out HC, CO, and NOx emissions during cold-start operation and during stoichiometric engine operation. Known LNT devices operate to reduce NOx emissions during lean engine operation by adsorbing NOx during lean operation and desorbing and reducing the stored NOx to nitrogen during rich operation. Known LNT devices have a temperature range of operation of about 250° C. to 450° C., with effectiveness decreasing above and below that temperature range. Known LNT devices experience thermal damage when exposed to exhaust gas feedstream temperatures of about 850° C., reducing effectiveness of the LNT device. Effectiveness of known LNT devices can be reduced due to exposure to elements present in fuel, including sulfur.

SUMMARY

An apparatus includes a spark-ignition, direct-injection internal combustion engine selectively operative at an air/fuel ratio lean of stoichiometry and directly fluidly connected to an exhaust aftertreatment system. The exhaust aftertreatment system consists essentially of an electro-thermal heating element adjoining a converter element wherein no other exhaust aftertreatment devices are disposed between the engine and the exhaust aftertreatment system. A control system therefore includes a control module signally connected to a sensing device adapted to monitor a temperature of the converter element and operatively connected to the engine and operative to connect the electro-thermal heating element to an electric power source.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described, by way of example, with reference to the accompanying drawings, in which:

FIGS. 1 and 2 are schematic diagrams of engine and exhaust aftertreatment systems, in accordance with the present disclosure.

DETAILED DESCRIPTION

Referring now to the drawings, wherein the showings are for the purpose of illustrating certain exemplary embodiments only and not for the purpose of limiting the same, FIGS. 1 and 2 schematically depict an internal combustion engine 10, control module 5, and exhaust aftertreatment system 45 that have been constructed in accordance with embodiments of the disclosure. Like numerals refer to like elements in the embodiments. Four embodiments of the exhaust aftertreatment system 45 are described herein, referred to as 45A, 45B, 45C, and 45D. The exemplary engine 10 comprises a multi-cylinder spark-ignition, direct-injection, four-stroke internal combustion engine operative in a repetitive combustion cycle comprising intake, compression, power, and exhaust strokes. The engine 10 is selectively operative at a stoichiometric air/fuel ratio and at an air/fuel ratio that is primarily lean of stoichiometry. The disclosure can be applied to various internal combustion engine systems and combustion cycles.

The engine 10 comprises a plurality of cylinders having reciprocating pistons 14 slidably movable therein, and a cylinder head 15. The cylinder, piston 14 and cylinder head 15 define a variable volume combustion chamber 16. Each piston 14 is connected to a rotating crankshaft 12 by which the linear reciprocating motion of the piston 14 is translated to rotational motion at the crankshaft 12. A crank sensor 13 monitors rotational position and speed of the crankshaft 12. One or more intake valves 20 controls air flow from an intake passage 29 into each of the combustion chambers 16. One or more exhaust valves 18 controls flow of exhaust gases from each of the combustion chambers 16 to an exhaust manifold 40 via an exhaust passage 39. Openings and closings of the intake and exhaust valves 20 and 18 are preferably controlled with a dual camshaft (as depicted), the rotations of which are linked and indexed with rotation of the crankshaft 12.

An air intake system provides intake air to an intake manifold 30 which directs and distributes air into the intake passage 29 leading to the combustion chamber 16 past the intake valve(s) 20 when opened. The air intake system comprises airflow ductwork and devices for monitoring and controlling the air flow to the intake passage 29. The devices preferably include a mass airflow sensor 32 for monitoring mass airflow and intake air temperature. A throttle valve 34 preferably comprises an electronically controlled device which controls air flow to the engine 10 in response to a control signal (‘ETC’) from the control module 5. A pressure sensor 36 in the intake manifold 30 is adapted to monitor manifold absolute pressure and barometric pressure. An external flow passage (not shown) recirculates exhaust gas from the exhaust passage 39 to the intake manifold 30, having a flow control valve comprising an exhaust gas recirculation valve 38 (hereafter ‘EGR valve’). The EGR valve 38 preferably comprises a controllable variable flow valve that is controlled by a control signal (‘EGR’) output from the control module 5.

A fuel injection system comprises a plurality of fuel injectors 28, each adapted to directly inject a mass of fuel into one of the combustion chambers 16, in response to a control signal (‘INJ_PW’) from the control module 5. The fuel injectors 28 are supplied pressurized fuel from a fuel distribution system (not shown). Each of the fuel injectors 28 is operative to inject the mass of fuel into the combustion chamber 16 in a single pulse per combustion cycle, or in multiple pulses per combustion cycle. A cylinder charge is formed in each combustion chamber 16 during each activated cylinder event by combining the injected fuel, the intake air, and residual and recirculated exhaust gases.

A combustion sensor 24 preferably monitors a state of combustion in the combustion chamber 16.

A spark-ignition system comprising an ignition module (not shown) and a spark plug 26 generates spark energy in the combustion chamber 16 for igniting or assisting in igniting a cylinder charge in response to an ignition signal (‘IGN’) from the control module 5. Under specific operating conditions the spark-ignition system can be disabled, permitting controlled auto-ignition operation of the engine 10.

The exhaust manifold 40 fluidly connects to an exhaust downpipe 48 which directly fluidly connects to the exhaust aftertreatment system 45. That is to say, no other exhaust gas aftertreatment device (e.g. close-coupled three-way catalyst) is intervening between the engine and the exhaust aftertreatment system 45. The exhaust gas feedstream flows from the exhaust valve 18 of the engine 10 through the exhaust manifold 40 to the exhaust downpipe 48 directly to the exhaust aftertreatment system 45 and preferably through a noise attenuation system (not shown) to atmosphere. A first sensor 42 monitors the engine-out exhaust gas feedstream, preferably monitoring a state of a parameter correlatable to engine-out air/fuel ratio, and a constituent of engine-out exhaust gas.

The exhaust aftertreatment system 45 is preferably located in an underfloor location of the vehicle out of the engine compartment of the vehicle, such that a converter element 46 of the exhaust aftertreatment system 45 is located at a predetermined distance from the exhaust valve 18 with no other exhaust gas aftertreatment device intervening between the engine and the exhaust aftertreatment system 45. The predetermined distance from the exhaust valve 18 for a given application is determined such that the exhaust gas feedstream temperature entering the converter element 46 is less than about 750° C. during normal engine operation. Thus, under normal engine operation is meant to encompass achievable speed/load operating points and controllable air/fuel ratios of the engine 10. The engine speed can range from an engine idle speed to engine redline, typically about 600 RPM to 7000+ RPM, engine loads can range from a closed throttle condition to a wide-open throttle condition, e.g., BMEP ranging from 0 bar to greater than 13 bar, and air/fuel ratios can range from a rich air/fuel ratio to a lean air/fuel ratio operation. By way of example, in one application the converter element 46 is placed at a distance of about 0.7 meters from the exhaust valve 18 of the engine 10 in order to ensure that the temperature of the exhaust gas feedstream entering the converter element 46 is less than about 750° C. during the normal engine operation and sustained wide-open throttle operation. The normal engine operation excludes engine operation in the presence of an engine fault leading to misfiring or misfueling in one or more of the combustion chambers 16.

A second sensor 50 monitors the exhaust gas feedstream downstream of the exhaust aftertreatment system 45. The monitoring of the exhaust gas feedstream includes, e.g., monitoring a state of a parameter correlatable to the engine-out air/fuel ratio, monitoring a constituent of the exhaust gas feedstream, or monitoring an operating characteristic of the exhaust aftertreatment system 45, e.g., temperature. The second sensor 50 preferably generates an output signal monitored by the control module 5. The signal output from the second sensor 50 can be used for control and diagnostics of the engine 10 and the exhaust aftertreatment system 45.

A third sensor 52, preferably comprising a temperature sensor, is positioned in the converter element 46 for monitoring an operating temperature thereof. The third sensor 52 preferably generates an output signal monitored by the control module 5.

A heating element 44 preferably comprises an electro-thermal device including an electroresistive metal-foil substrate having a cell structure with a multiplicity of flow-through cells. Density of the flow-through cells is preferably about 16-186 cells per square centimeter (100-1200 cells per square inch). Electric current is passed through the heating element 44 through electrodes 47. The electric current through the electrodes 47 is controlled via a current control device 49. The current control device 49 preferably comprises a high-power switching device, e.g., a power transistor, which connects electric power from a vehicle electrical system (‘V+’) to the electrodes 47 in response to a control signal (‘EHC_PWM’) output from the control module 5. The heating element 44 transfers heat to the exhaust gas feedstream via radiant and conductive heat transferring to the exhaust gas feedstream in contact therewith. A washcoat including catalytically active materials, e.g., platinum-group metals (hereafter ‘PGM’), e.g., Pt, Pd, and Rh, is preferably chemically deposited onto the surface of the metal-foil substrate of the heating element 44.

The first embodiment of the exhaust aftertreatment system 45A includes the heating element 44 and the converter element 46. There is no other exhaust gas aftertreatment device intervening between the engine and the exhaust aftertreatment system 45B. The converter element 46 includes a catalyzed NOx adsorber, wherein a substrate (not shown) is coated with catalytically active material, referred to as a lean-NOx reduction catalyst. The substrate preferably comprises a monolithic element formed from cordierite with a cell density about 62 to 93 cells per square centimeter (400-600 cells per square inch), and a wall thickness about three to seven mils. The cells of the substrate comprise flow passages through which exhaust gas flows to contact the catalytically active materials to effect adsorption and desorption of nitrates, oxygen storage, and oxidization and reduction of constituents of the exhaust gas feedstream. The substrate is preferably coated with a washcoat containing alkali and/or alkali earth metal compounds, e.g., Ba and K, operative to adsorb NOx as nitrates generated during lean engine operation. The washcoat also contains catalytically active materials, e.g., PGMs comprising Pt, Pd, and Rh, and additives (e.g., Ce, Zr, La). Under rich engine operation, there are excess reductants (CO, H2, HC) in the exhaust gas feedstream, and the adsorbed nitrates are desorbed. The desorbed nitrates are reduced by the excess reductants at catalytically active sites. Exemplary loadings for Ba and K are about 5-25 wt %, and exemplary PGM loadings are Pt: 30-120 g/ft3; Pd: 5-50 g/ft3, and Rh: 3-20 g/ft3. Platinum is required for oxidation of NO to NO2, a necessary step for nitrate formation as engine-out NOx typically consists of >90% NO. An exemplary working temperature window for the converter element 46 including the catalyzed NOx adsorber is about 250° to 500° C. At converter element 46 temperatures that are less than about 250° C., NO to NO2 oxidation kinetics are too slow to effectively oxidize the nitrates in the exhaust gas feedstream, and the NOx reduction kinetics under engine operation that is rich of stoichiometry are too slow to effectively regenerate NOx storage sites in a timely manner during ongoing engine operation. At temperatures greater than about 500° C., the nitrate becomes unstable even under engine operation that is lean of stoichiometry, making the converter element 46 unable to efficiently store nitrates. Therefore maintaining the converter element 46 within the working temperature window is desirable for NOx reduction at a level necessary to achieve emissions targets. The washcoat adsorbs NOx molecules during lean engine operation, and desorbs and reduces NOx molecules during engine operation that generates a rich exhaust gas feedstream. The control module 5 selectively controls the engine 10 at a rich air/fuel ratio for a period of time. The period of time for rich operation is determined based upon an elapsed time necessary to desorb the adsorbed NOx from the converter element 46, upon size of the converter element 46 and upon other factors. The converter element 46 functions as a three-way catalyst at stoichiometric engine operating conditions in the presence of the PGMs and the Ce and Zr washcoat components.

The second embodiment of the exhaust aftertreatment system 45B includes the heating element 44 and converter element 46′. Here, as with the other embodiments, there is no other exhaust gas aftertreatment device intervening between the engine and the exhaust aftertreatment system 45B. The converter element 46′ comprises a particulate filter in combination with a lean-NOx reduction catalyst, also referred to as a particulate filter NOx reduction device (‘PNR’). The ceramic substrate (not shown) preferably comprises a monolithic cordierite substrate with a cell density about 31 to 47 cells per square centimeter (200-300 cells per square inch), and a wall thickness of three to seven mils. Alternating cells of the substrate are plugged at one end. The walls of the substrate have high porosity (e.g., about 55% porosity or higher with a mean pore size of about 25 microns) to allow for flow of exhaust gases and impregnation of NOx adsorber catalysts. The ceramic substrate is preferably coated with a washcoat containing alkali and alkali earth metal compounds, e.g., Ba and K, operative to store NOx as nitrates that are generated during engine operation that is lean of stoichiometry. The washcoat also contains catalytically active materials, i.e., the PGM comprising Pt, Pd, and Rh, and additives (e.g., Ce, Zr, La).

The third embodiment and fourth embodiments of the system are depicted in FIG. 2. The third and fourth embodiments also have no other exhaust gas aftertreatment device intervening between the engine and the respective exhaust aftertreatment systems 45C or 45D. The third embodiment of the exhaust aftertreatment system 45C includes the heating element 44, the converter element 46 comprising lean-NOx reduction catalyst, and a selective catalytic reduction device 60. The fourth embodiment of the exhaust aftertreatment system 45D includes the heating element 44, the converter element 46′ including the particulate filter NOx reduction device and the selective catalytic reduction device 60. The selective catalytic reduction device 60 comprises a zeolite catalyst including of a ceramic substrate coated with washcoat with one of Cu and Fe ion-exchanged into a zeolite lattice structure. The substrate comprises a monolithic structure with a cell density about 62 to 93 cells per square centimeter (400-600 cells per square inch), and a wall thickness about 3 to 7 mils. The selective catalytic reduction device 60 functions to adsorb gaseous ammonia released during regeneration of the lean-NOx reduction catalyst. The third and fourth embodiments each can include a fourth sensor 50′ operative to monitor the exhaust gas feedstream downstream of the selective catalytic reduction device 60. The monitoring of the exhaust gas feedstream includes, e.g., monitoring a state of a parameter correlatable to the engine-out air/fuel ratio, monitoring a constituent of the exhaust gas feedstream, or monitoring an operating characteristic of the exhaust aftertreatment system 45, e.g., temperature. The fourth sensor 50′ preferably generates an output signal monitored by the control module 5 which can be used for control and diagnostics of the engine 10, the exhaust aftertreatment system 45, and the selective catalytic reduction device 60. The fourth sensor 50′ can be used in conjunction with the second sensor 50, or in place of the second sensor 50.

The control module 5 comprises a general-purpose digital computer including a microprocessor or central processing unit, storage mediums comprising non-volatile memory including read only memory (ROM) and electrically programmable read only memory (EPROM), random access memory (RAM), a high speed clock, analog to digital (A/D) and digital to analog (D/A) circuitry, input/output circuitry, and devices (I/O) and appropriate signal conditioning and buffer circuitry. The control module 5 has a set of control algorithms, comprising resident program instructions and calibrations stored in the non-volatile memory and executed to provide the respective functions for controlling the engine 10. The algorithms are typically executed during preset loop cycles such that each algorithm is executed at least once each loop cycle. Algorithms are executed by the central processing unit and are operable to monitor inputs from the aforementioned sensing devices and execute control and diagnostic routines to control operation of the actuators, using preset calibrations. Loop cycles are typically executed at regular intervals, for example each 3.125, 6.25, 12.5, 25 and 100 milliseconds during ongoing engine and vehicle operation. Alternatively, algorithms may be executed in response to occurrence of an event.

In operation, the control module 5 monitors inputs from the aforementioned sensors to determine states of engine parameters. The control module 5 executes algorithmic code stored therein to control the aforementioned actuators to form the cylinder charge, including controlling throttle position, spark-ignition timing, fuel injection mass and timing, EGR valve position to control flow of recirculated exhaust gases, and intake and/or exhaust valve timing and phasing on engines so equipped. The control module 5 can operate to turn the engine 10 on and off during ongoing vehicle operation, and can operate to selectively deactivate one or more of the combustion chambers 16 through control of fuel and spark.

The engine 10 is preferably operated lean of stoichiometry under low load driving conditions and idling, and at stoichiometric operation under high speed, high load conditions. During lean operations the engine is preferably controlled to an air/fuel about 25:1 to 40:1 for gasoline. Elevated exhaust gas feedstream temperatures can be achieved during engine warm-up, e.g., subsequent to a cold-start, by operating the engine 10 with retarded spark timing and multiple fuel pulses per combustion event. The control module 5 can control the engine 10 to elevate the exhaust gas feedstream temperature and operate the heating element 44 through actuation of the current control device 49 to rapidly heat up the converter element 46 based upon predetermined conditions, e.g., when the third sensor 52 indicates the temperature of the converter element 46 is less than a preferred temperature for optimum efficiency.

The control module 5 executes algorithmic code to determine state(s) of exhaust gas feedstream parameter(s) based upon the output of the first sensor 42 and predetermined calibrations stored in a memory device in the control module 5, for controlling the engine 10 and monitoring operation of the engine 10.

The control module 5 executes algorithmic code to determine state(s) of exhaust gas feedstream parameter(s) and the exhaust aftertreatment system 45 based upon the signal outputs of the first sensor 42 the second sensor 50, the third sensor 52, the fourth sensor 50′ (where used), and predetermined calibrations stored in the memory device in the control module 5, for monitoring operation of the engine 10 and the exhaust aftertreatment system 45 including engine control and diagnostics.

In operation, after cranking and starting the engine 10, the control module 5 controls operation of the engine 10 and operation of the current control device 49 to heat the exhaust aftertreatment system 45. This preferably includes operating the engine 10 using multiple fuel injection pulses for each combustion chamber 16 for each combustion event, and retarded spark-ignition timing to increase temperature of the exhaust gas feedstream. Simultaneously, the control module 5 controls the current control device 49 to transfer electrical power to the heating element 44. This is referred to as a catalyst warm-up mode. The control module 5 monitors signal input from the third sensor 52, and when the third sensor 52 indicates that the temperature of the converter element 46 exceeds a predetermined threshold, e.g., about 300° C., the control module 5 discontinues controlling the current control device 49, and controls the operation of the engine 10 in a normal engine operating mode to optimize power and fuel economy, and discontinuing the catalyst warm-up mode. The control module 5 can crank and start the engine 10 multiple times during a single trip when employed on a vehicle operative in an engine stop/start mode, e.g., on a vehicle employing a hybrid powertrain system.

Conversion efficiencies of the converter element 46 can be reduced due to deposition of sulfur on the surface of the catalyst substrate. Compounds that form stable nitrates, e.g., alkali and alkali earth metal compounds, form stable sulfate. Thus, NOx storage components in the converter element 46 form sulfates with exposure to sulfur compounds in the exhaust stream, reducing NOx storage capacity thereof. Sulfur is removed from the converter element 46 through a process called desulfation, which is periodically commanded based upon engine operating conditions and sulfur content in the fuel. The desulfation process includes controlling operation of the engine 10 and the heating element 44 to heat the converter element 46 to an elevated temperature, typically greater than about 700° C., and expose the converter element 46 to a rich exhaust gas feedstream. The heating element 44 and engine are controlled to achieve the elevated temperature and rich air/fuel ratio exhaust gas feedstream for a period of time to desulfate the converter element 46, preferably without affecting engine output torque.

The disclosure has described certain preferred embodiments and modifications thereto. Further modifications and alterations may occur to others upon reading and understanding the specification. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims. 

1. Apparatus, comprising: a spark-ignition, direct-injection internal combustion engine selectively operative at an air/fuel ratio lean of stoichiometry and directly fluidly connected to an exhaust aftertreatment system; the exhaust aftertreatment system consisting essentially of an electro-thermal heating element adjoining a converter element wherein no other exhaust aftertreatment devices are disposed between the engine and the exhaust aftertreatment system; and a control system comprising a control module signally connected to a sensing device adapted to monitor a temperature of the converter element and operatively connected to the engine and operative to connect the electro-thermal heating element to an electric power source.
 2. The apparatus of claim 1, comprising the exhaust aftertreatment system located at a distance from the engine such that a temperature of the exhaust gas feedstream entering the converter element is less than 750° C. during normal engine operation.
 3. The apparatus of claim 2, further comprising the converter element located at a distance at least 0.7 meters from an exhaust valve of the internal combustion engine.
 4. The apparatus of claim 1, wherein the converter element comprises a ceramic substrate having a washcoat containing at least one of a metal consisting of platinum, palladium, and rhodium and an alkali and/or alkali earth metal compound consisting of one of barium and potassium.
 5. The apparatus of claim 1, comprising the control module operative to control a current control device to connect the electro-thermal heating element to the electric power source when the signal output from the sensing device indicates the temperature of the converter element is less than a predetermined threshold.
 6. The apparatus of claim 5, further comprising the control module operative to selectively control the internal combustion engine at an air/fuel ratio rich of a stoichiometric air/fuel ratio and operative to connect the electro-thermal heating element to the electric power source to control the temperature of the exhaust gas feedstream entering the converter element to about 700° C. for a predetermined period of time to desulfate the converter element.
 7. The apparatus of claim 5, further comprising the control module operative to selectively connect the electro-thermal heating element to the electric power source when the engine is shutdown during ongoing vehicle operation.
 8. The apparatus of claim 1, further comprising the control module operative to selectively control the internal combustion engine at a stoichiometric air/fuel ratio for a period of time determined to substantially desorb the adsorbed NOx from the converter element.
 9. The apparatus of claim 1, wherein the electro-thermal heating element comprises a metal-foil substrate having a washcoat chemically deposited onto the surface thereof.
 10. The apparatus of claim 9, wherein the washcoat includes catalytically active material.
 11. Apparatus, comprising a spark-ignition, direct-injection internal combustion engine selectively operative at an air/fuel ratio lean of stoichiometry and directly fluidly connected to an exhaust aftertreatment system; the exhaust aftertreatment system consisting essentially of an electro-thermal heating element adjoining a catalyzed NOx adsorber device wherein no other exhaust aftertreatment devices are disposed between the engine and the exhaust aftertreatment system; and a control system comprising a control module signally connected to a sensing device adapted to monitor a temperature of the converter element and operatively connected to the engine and operative to connect the electro-thermal heating element to an electric power source.
 12. The apparatus of claim 11, wherein the catalyzed NOx adsorber device comprises a monolithic substrate having a washcoat containing at least one of a metal consisting of platinum, palladium, and rhodium and containing an alkali metal compound consisting of one of barium and potassium.
 13. The apparatus of claim 11, further comprising the control module operative to selectively control the internal combustion engine at a stoichiometric air/fuel ratio for a period of time determined based upon desorption of adsorbed NOx from the converter element.
 14. Apparatus, comprising: a spark-ignition, direct-fuel injection internal combustion engine selectively operative at an air/fuel ratio lean of stoichiometry and directly fluidly connected to an exhaust aftertreatment system; the exhaust aftertreatment system consisting essentially of an electro-thermal heating element adjoining a particulate filter NOx reduction catalyst wherein no other exhaust aftertreatment devices are disposed between the engine and the exhaust aftertreatment system; and a control system comprising a control module signally connected to a sensing device adapted to monitor a temperature of the converter element and operatively connected to the engine and operative to connect the electro-thermal heating element to an electric power source.
 15. The apparatus of claim 14, further comprising the control module operative to selectively control the internal combustion engine at an air/fuel ratio rich of a stoichiometric air/fuel ratio and operative to connect the electro-thermal heating element to the electric power source to control the temperature of the exhaust gas feedstream entering the converter element to about 700° C. for a period of time determined to purge carbon from the converter element.
 16. Apparatus, comprising a spark-ignition, direct-injection internal combustion engine selectively operative at an air/fuel ratio lean of stoichiometry and directly fluidly connected to an exhaust aftertreatment system; the exhaust aftertreatment system consisting essentially of an electro-thermal heating element adjoining a converter element and a selective catalytic reduction element wherein no other exhaust aftertreatment devices are disposed between the engine and the exhaust aftertreatment system; and a control system comprising a control module signally connected to a sensing device adapted to monitor a temperature of the converter element and operatively connected to the engine and operative to connect the electro-thermal heating element to an electric power source.
 17. The apparatus of claim 16, comprising the exhaust aftertreatment system located at a distance from the engine such that a temperature of the exhaust gas feedstream entering the converter element is less than 750° C. during normal engine operation.
 18. The apparatus of claim 17, wherein the converter element comprises one of a particulate filter NOx reduction catalyst and a catalyzed NOx adsorber device.
 19. The apparatus of claim 17, wherein the selective catalytic reduction element comprises a substrate having zeolite and one of copper and iron coated thereon.
 20. The apparatus of claim 19, wherein the control system further comprises a sensing device operative to monitor the exhaust gas feedstream downstream of the exhaust aftertreatment system. 